Biosensors have recently become known for their ability to simultaneously quantify many different biomolecular interactions with high sensitivity. The technology has been developed to detect a variety of biomolecular complexes including oligonucleotides, antibody-antigen interactions, hormone-receptor interactions, and enzyme-substrate interactions. These tools have enormous capability for applications in pharmaceutical discovery, proteomics, and diagnostics. Further, for these tools to find widespread use, they should be applicable to a wide range of analytes that can include, for example, polynucleotides, peptides, small proteins, antibodies, and even entire cells.
Typically, the technology involves using a grating-couple waveguide (GCW) to sense a concentration change, surface adsorption, reaction, or the presence of a biological or chemical substance at the GCW surface. An optical interrogation system uses optical elements, such as a grating, to couple a light beam from a light source in and out of an optical mode in the waveguide of the GCW sensor. The angle or wavelength of the emitted light beam is detected and analyzed to determine the effective refractive index of the waveguide. Changes in the angle or wavelength of the probe light, for example, indicate changes of the waveguide effective index that result from activity at the sensor surface. In particular, GCW sensors are advantageous for use in high-throughput screening applications. When applied in the context of the microplate, the waveguide and diffraction grating of the GCW sensor are preferably located in the bottom of each well (e.g., the diffraction grating may be stamped or otherwise molded into the well bottom, and the waveguide is subsequently applied on top of the diffraction grating). Specifically, the sensor is located in the center of a bottom surface of each well.
A process for replicating the grating structures onto a glass or plastic substrate has been through the use of a UV curable material in combination with a preformed tool or mold. Two such processes are known as UV embossing (typically a dynamic process), or UV cast and cure (generally static process). In the UV embossing or cast and cure processes, a UV curable liquid material composition is dispensed or transferred onto either the substrate or the tool containing the optical features or between the substrate and the tool. Then, the composition is cured with UV radiation such that either the substrate or the tool allows transmission of the radiation. The tool and the substrate are then separated with the cured composition replicating the optical features of the tool surface and remaining adhered to the substrate.
Unfortunately, commercially available UV curable materials contain undesirable urethane(meth)acrylates, halogenated (meth)acrylates, or monofunctional acrylates. The manufacture and performance of micro and nano size optical gratings made from these acrylate materials has been poor, due to undesirable viscosity of the fabrication material and unacceptable changes in surface tension. As well, excessive shrinkage produces an undesirable warpage or distortion of the grating and/or substrate.
There remains a need in the art for three-dimensional, polymeric optical elements that can be manufactured with a high degree of precision and enhanced consistency. In order to be useful in these applications, a photo or electron beam curable composition will be especially suited for flowing into the fine micro or nano size structures of a mold/tool. In particular, the improved photocurable composition will have a low viscosity and allow for rapid, facile replication of micro or nano sized features with high fidelity. Additionally, minimal surface tension effects will allow formation of a variety of shapes and ranges of micro- or nano-size patterns onto a substrate. The improved organic optical component, fabricated using a photo or EB curable composition, will easily release from the tool and be transferred, or adhered, to the substrate, instantly replicating the micro or nano size features from the tool. Furthermore, since the waveguide coating deposition process may involve exposure of the grating material to somewhat high temperatures (≧70° C.), it is desirable that the glass transition temperature (Tg) of the grating material be higher than this temperature. As well, the waveguide coating deposition process may also be done under vacuum. It is therefore desirable that the grating material not appreciably oxidize or evolve volatile material during this process. Subsequently, the cured product will be an optically clear material with minimal shrinkage, low outgassing, and low extractables. As desired, a photocurable composition and method of using the composition will be capable of satisfying these stringent requirements.